Pumps used in aquariums are well known. Their function is to make the water circulate through an undergravel filter, and also to oxygenate the water. The usual pump includes an impeller, generally of the centrifugal type, driven by an electrical synchronous motor.
A major drawback of known aquarium water circulation pumps is that they do not provide any indication of the water flow rate through the pump. This is important at the time of regulation in order to create the best water change conditions relative to the dimensions of the aquarium. Also, it is important at the time of verification in order to determine, from the indications of the flow rate, the clogging conditions of the filter. However, adopting an independent instrument to measure the flow rate of an aquarium water circulation pump is not justifiable because of the relatively high cost involved for that particular usage.
It is also generally known to provide aquarium water circulation pumps with an adjustable valve at the pump inlet to regulate the water flow rate through the pump. However, to adjust the valve usually requires a person to immerse his or her hand in the water to reach the valve, making it difficult to adjust.
It has been suggested to provide a separate control shaft for the valve, with an actuator knob on the upper end and suitable gearing on the lower end for operating the valve by rotating the knob externally of the water. However, the required number of parts and complexity of such an assembly makes it too costly to be practical.
Furthermore, it is generally known to oxygenate the water being circulated in an aquarium according to the Venturi effect, by causing the water to flow through a narrowing passage to increase the water speed and thereby reduce the pressure. By ending an external air tube in this narrow passage, the reduction in water pressure at this point creates a suction effect causing air to be drawn through the tube and mixed with the water. A disadvantage of this known method of water oxygenation is that it requires the use of an additional tube which is aesthetically unsightly and adds to the cost of the assemblage. Moreover, its function, based on the Venturi principle, requires a certain speed in the water recycling, thus creating the need for a motor of a certain range just to activate the pump. Furthermore, the Venturi effect creates an undesirable turbulence where the water is readmitted in the aquarium.